Do you have a place you can run that fast without being in danger of running into something in case something goes wrong. That is the one thing that is stop me from getting a car that will do those kind of speeds. All it takes is one little bump in the road and you're done.
If you run a lower KV motor with higher voltage you're just going to add a lot of weight to the car. That might be something you want if you're looking to get the speed in order to keep from getting airborne. If you go with a higher KV motor and lower voltage you'll have a lighter car unable to...